I've owned both of the ones mentioned not to mention most other high end electronics. I did a lot of power supply design for most of the companies I have mentioned along with others on a contract basis in the 80s. Had the opportunity to meet both Harvey Rosenberg and Bill Johnson along with Dan D'Agostino of Krell, etc. Used to work for free but got a lot of cool equipment that only the very well heeled could afford. I loved the simplicity of the OTL circuit but it was useless unless the speaker impedance was quite high and capacitive. That is why the Quad ESLs and other electrostatics were a good match. However, I was not a big fan of chamber music and the lack of bass was troubling. I did run Martin Logan monoliths using SA4s for the panels and a solid state Krell to drive the woofer. That was a sweet setup.
None of these animals are what I would call "reliable". When a tube goes, it can be catastrophic. Some of these amplifiers also were a bear to repair as many had point to point wiring. ARC really pioneered "mass production" of tube amplifiers if you could ever call it that. I stopped using large tube amps due to the difficulty of finding matched tubes for reasonable prices. True the Chinese and Russians still make tubes but try to find a matched octet of 6550s for one side of an ARC D250 or matched 6LF6 tubes for an SA-4. You can get them but the costs are really outrageous. Maybe Western Electric's resurgence will change that.
Tube phono stages and preamps were the sweet spot for me. Hook up an ARC 10 preamp to a pair of KRELL mono blocks and connect to any speaker you desire without regard to the impedance. There is nothing like Class A power to drive complex speaker loads. Of course, your source had better be good or you will be disappointed. The source is the first link. Drop the ball there and it really don't matter what you use.
Those were good days but after a lifetime of shooting and other loud pastimes, my ears no longer warrant any gear like this.
